Objective: The purpose of this study was to evaluate the phase stability, surface characteristics, hardness and flexural strength of Yttrium stabilised zirconia ceramics after various low temperature aging using X-ray diffraction analysis, Scanning Electron Microscopy, a micro hardness tester and a universal testing machine respectively. Materials and methods: Blocks of Y-TZP from two manufacturers (n=15) Group-A AIDITE (Qinhuangdao Technology Co., Ltd, Hebei, China) and Group-B UPCERA(Shenzhen Upcera Dental Technology Co. Ltd, Guangdong, China) were machined, sintered and glazed according to manufacturer’s specifications. These were of 40mm (length)×5mm (width)×3mm (height). Specimens were artificially aged in distilled water by heat treatment at 100°C, 150°C and 200°C for 10 hours each to induce phase transformation. These specimens after aging were individually evaluated for the phase transformation using X- ray diffraction (JDX 8P, JEOL machine) and surface characteristics using scanning electron microscopy (6380 LA, JEOL machine). They were also evaluated for hardness using micro hardness tester (Reichert Austria micro hardness tester) and flexural strength using universal testing machine (Unitest-10). Results: The results from x-ray diffraction analysis of both the specimens with and without low temperature aging revealed only the tetragonal phase. On scanning electron microscopy, the surface of the specimens in as received condition appeared to be smooth with a few blebs here and there. As aging was carried out, the surface irregularities became more pronounced. Hardness testing showed that the hardness was highest without aging as compared to when aging was carried out. There was a considerable decrease in hardness in group B when compared to group A. The results from flexural strength evaluation showed that in group A, there was a decrease in the mean flexural strength when aging was carried out. The flexural strength in group B kept fluctuating and was the highest when aged at 100°C. A sudden decrease in the flexural strength was noted when aged at 150°C. Conclusion: The in vitro tests conducted reveal that the two materials Aidite and Upcera did not show significant results on x-ray diffraction analysis and scanning electron microscopy. These tests also reveal that when low temperature aging was carried out at a temperature of 100°C for 10 hours, the hardness of Y-TZP ceramics decreased whereas the flexural strength increased. However, beyond this temperature of 100°C especially at 150°C and above, the flexural strength of both the materials started to decrease.
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